Surface and deep ocean circulation through time- LGM

Question 1

Evidence for ice activity-indicating ice movement

Answer 1

• Erratic boulders
• Striae

Question 2

What controls long-term climate chage?

Answer 2

Variation in Earth’s orbital parameters- Milankovitvh theory

Question 3

Eccentricity

Answer 3

Variation of the Earth’s path around the sun- 100ka and 400ka

Question 4

Obliquity

Answer 4

Variation of Earth’s rotational axis with respect to its rotational plane around the sun- 41ka

Question 5

Precession

Answer 5

Wobble of the rotational axis - 19-24 ka

Question 6

1-6% eccentricity (circular to elliptical)

Answer 6

Takes 100,000 years

Question 7

Aphelion

Answer 7

Distant path position to the sun

Question 8

Perihelion

Answer 8

Close path position to the sun

Question 9

Earth’s axial tilt varies from 24.5 to 22.1 degrees

Answer 9

Every 41,000 years

Question 10

What impact does axial tilt (obliquity) have?

Answer 10

Effects the distribution of solar radiation on Earth’s surface- when tilt decreases, polar regions receive less sunlight

Question 11

Impact of changing precession?

Answer 11

Alters which hemisphere receives more sunlight during the summer

Question 12

Evidence for the Milankovitch cycles?

Answer 12

Assemblages of particles (biogenic or lithogenic) within the ocean- sedimentation

Question 13

Most frequently used ‘tool’ used to reconstruct ocean circulation patterns

Answer 13

Planktonic and benthic foraminifera

Question 14

Oxygen isotopes incorporated in foraminifera that reflect T an S of sea water

Answer 14

18O and 16O incorporated as part of the CaCO3 test

Question 15

Two carbon isotopes incorporated into the test of foraminifera

Answer 15

13C and 12C

Question 16

The older the water mass…

Answer 16

The higher the 12C concentration in the water and the foraminifera tests

Question 17

Which C isotope end up in organic tissue in a higher amount?

Answer 17

12C

Question 18

When organisms die…

Answer 18

Organic matter sinks to the floor taking 12C rich tissue with it- extracting 12C from the surface ocean and oxidizing organic matter on its way down the water column and releasing 12C back into the ocean at depth= BIOLOGICAL PUMPING

Question 19

NADW- isotope values

Answer 19

NADW starts with high carbon isotope values- on its way towards the Pacific–> addition of 12C by oxidizing organic matter DECREASES CARBON ISOTOPE VALUES

Question 20

Carbon isotope signature of AABW

Answer 20

Very low carbon isotope values

Question 21

Oxygen isotope- evaporation

Answer 21

During evaporation 18O and 16O enter the vapor phase at a different rate. 16O more enriched in water vapor that 18O

Question 22

16O evaporation

Answer 22

Evaporates much quicker than 18O

Question 23

Oxygen isotopes in foraminifera are controlled by 3 parameters:

Answer 23

1. Temperature
2. Variation in size of continental ice masses
3. oxygen isotopes of the ambient seawater (out of which the foraminifera calcifies its test)

Question 24

Difference in oxygen isotope values between surface and deep ocean:

Answer 24

Reflect the temperature gradient between surface and deep ocean

Question 25

Change in oxygen values in foraminiera with temp?

Answer 25

Warmer temps= favour 16O incorporated into CaCO3 test Colder temps= favour 18O

Question 26

Consequences of waxing and waning of continental ice masses for the ocean:

Answer 26

1. A lot of 16O extracted from ocean and stored in the ice leading to higher oxygen isotopes in water 2. Extracted water led to lowered sea level

Question 27

Piston Corer

Answer 27

Can retrieve sediment cores from the soft seabed to depths of 30m. The piston prevents water from entering the core barrel- preserving sediment layers

Question 28

Gravity Corer

Answer 28

Retrieves sediment cores from soft- medium firm sediments from a few m to tens of m. Lowered and collected sample by its weight - cheaper than piston corer but shorter samples

Question 29

Box corer

Answer 29

Can collect LARGE UNDISTURBED sediment samples however only on the top layer of sea floor. Collection by weighted box and two hinged spade doors

Question 30

Multi corer

Answer 30

Multi corer for short sediment sequences. Provides excellent surfaces sediment/bottom water samples. Better than box corer, but more fragile, entailing risk of destruction. Length of sediment section depends on design (50-60cm max)

Question 31

Steps leading from LGM--> Holocene

Answer 31

1. Deglacial step- terminated LGM 2. B-A Oscillation 3. Younger Dryas (YD)

Question 32

B-A Oscillation

Answer 32

Bolling-Allerod Oscillation; two short warm pulses separated by a short cold event

Question 33

IRDs during the glaciation

Answer 33

Ice rafted debris (IRD) - icebergs drifted off to Portugal leaving a trail of IRD- implies meltwater being around at the sea surface

Question 34

Sediment transport associated with Heinrich events

Answer 34

IRD released from icebergs and suspended sediment in meltwater

Question 35

Surface ocean conditions-LGM

Answer 35

Much colder N.Atlantic with a few icebergs around an expanded sea ice cover --> Gulf Stream= weakened (most of the flow re-routed eastward)

Question 36

Meltwater world (Heinrich Event 1)

Answer 36

Cold in general, additional cooling in some locations, flotillas of icebergs around accompanied by meltwater

Question 37

The Holocene

Answer 37

Modern warm period

Question 38

Planktonic foraminifera

Answer 38

Reflect surface ocean conditions

Question 39

Benthic foraminifera

Answer 39

Reflect bottom ocean conditions

Question 40

Projection plane

Answer 40

Individual locations projected onto the projection plane according to location and water depth

Question 41

Sediment dating

Answer 41

Used to establish the rate a particular section has been deposited

Question 42

Time slice approach

Answer 42

Defining sediment sections that contain info from a specific time period

Question 43

NADW- LGM

Answer 43

The likely sources areas for glacial NADW shifted to an area south of Iceland

Question 44

Meltwater period (Heinrich Event 1) - NADW

Answer 44

Meltwater from ice caps melting reaches source areas of NADW reducing salinity- NADW formation REDUCES.

Question 45

Changes in T/S properties in the N-Atlantic

Answer 45

Large volume of ice= water volume reduced and salinity increased (1psu) - affects convention in areas of Deepwater formation

Question 46

Younger Dryas (YD)

Answer 46

Return to glacial conditions in less than 100 years --> Maybe caused by a reduction in North Atlantic Conveyer Belt